Add-on units are attached to standard analog or digital ultrasonic flaw detector instruments for either suppressing noise spikes that clutter up the flaw detectors"" screens or enhancing very weak, barely detectable signals. The add-on units may do both simultaneously as well. Each unit includes an adjustable filter so that a user may tune the filter bandwidth to a specific range within the overall transducer band that coincides with the signal to be either suppressed or enhanced.
Each adjustable filter may use a variable filter circuit. The filter has independent controls for frequency, bandwidth and null/gain adjustments. The unit also includes a pre-amplifier for boosting weak signals prior to filtering. The unit may be added to any ultrasonic non-destructive inspection/evaluation (UT NDI/E) equipment and operates independently of that equipment. The unit operates in any of the three UT NDI/E inspection modes: pulse-echo, pitch-catch and through-transmission. The unit operates on single signals and in real-time. The unit has a small enclosure so that it may be portable and operated by a battery or an ac adapter.
The new Noise Suppressor II (NSII) system combines three independent functions, two tunable filters and one pre-amplifier, into one unit that provides a means for either suppressing noise signals (spikes or background noise) or enhancing a signal of interest by increasing the signal/noise ratio, or both.
The system is used as an add-on module to ultrasonic pulser/receiver instruments. These instruments may be either analog or digital devices that are components in an overall ultrasonic (UT) non-destructive inspection/evaluation (NDI/E) system, or they may be stand-alone self-contained UT instruments, usually called flaw detectors, that are commonly used in either manual, semi-automated or fully automated UT NDI/E applications. Even though these UT instruments may have some built-in noise suppression and/or signal enhancement capabilities, these are usually fairly rudimentary and hard-wired such that the user has no choices other than those supplied by the instrument manufacturer. As an add-on module, the NSII system""s purpose is to enhance the function of the UT instrument by giving the user a set of signal filtering controls that are tunable to the particular needs of each application. As such, the NSII provides a significant increase in noise suppression and/or signal enhancement capabilities, all under user control.
The primary purpose of the NSII is to enhance signals returned from UT transducers being used as part of the NDI/E process. One of the main problems associated with UT flaw detector instruments is discriminating the response (either pulse-echo, pitch-catch or through-transmission) of a flaw from the background noise. Flaw detectors operate normally in a very wide band mode, whereas the signal returned from the transducer is much narrower in bandwidth. A simple narrow band filter may be used to substantially lower the noise floor and to enhance the signal/noise ratio.
One of the problems, however, is that the returned echo is not always centered on the same frequency as the built-in bandpass filter. The signal returned from the transducer is typically fairly wide band and different types of defects (i.e. targets) are represented in different bands of the incident signal. Also, UT transducers themselves may resonate at different frequencies and this varies with the type of transducer being used.
It is therefore highly desirable that the filter be tunable (i.e., adjustable) so that the user may xe2x80x9ctunexe2x80x9d the filter band to the specific range within the overall transducer band that coincides with the signal to be either suppressed or enhanced. This is similar to tuning a stereo receiver to find the optimal frequency position that delivers the best signal for a broadcasting station of interest. The NSII provides three functions that permit the user to tune either of the two filters"" bands: (1) center frequency of at least 0.5 MHz (preferably ranges between 0.5 to 1.3 MHz and between 1.5 MHz to 7 MHz), (2) width of the band (narrow, medium, wide), and (3) amplification, either positive or negative, in the band (Gain=+15 dB or Null=xe2x88x9220 dB). Frequency ranges of about 0.15 to about 25 MHz are provided by embodiments of the invention.
Noise suppression is desirable when the noisy signal(s) is(are) induced by the material or the flaw detector itself. Noise from external sources (i.e., environmental noise) can also present problems due to their superposition on the small return responses from defects and the subsequent need for high amplification in the UT instrument to detect these small signals. External noise can sometimes literally mask the signal of interest or at least make its detection very difficult. Examples of high-amplitude external noise sources include electrical noise from positioning motors of a scanning system and welding machines.
It is therefore desirable that the filter be able to remove certain frequency bands as well as enhance the main frequency. It is also necessary to vary the bandwidth of the filter to match the bandwidth of the desired signal or noise source to obtain optimal signal enhancement.
The NSII does all of these things over a frequency range compatible with most ultrasonic NDI/E testing: at least 0.5 MHz with preferred ranges of about 0.5 to 1.3 MHz and 1.5 MHz to 7 MHz, or about 0.15 to about 25 MHz. The effectiveness of the NSII is increased by including two filter elements that permit combinations of noise suppression, signal enhancement or both. In theory, more stages may be added until the filters start interfering with one another due to bandwidth considerations.
The NSII contains a pre-amplifier as a third independent function. The preamp is adjustable by the user over a 0 dB to 30 dB range, in steps of 10 dB. The preamp""s purpose is to boost weak signals (up to 30 dB) prior to any filtering operation(s) or to act as a stand alone additional amplification boost when no filtering is desired. This latter condition is commonly encountered when running long cable lengths between the UT transducer and its receiving UT instrument. The total gain of the system, therefore, is equal to 60 dB which derives from +30 dB in the preamp and +15 dB in each of the two filters if both filters are being used for signal enhancement.
The preferred Noise Suppressor II(trademark) is an add-on unit to ultrasonic pulser/receivers and flaw detectors. The unit can be set to either suppress noise (spikes or background) or to enhance the signal/noise ratio of weak desirable signals, or both.
The preferred Noise Suppressor II(trademark) combines three independent functions that can be used in any combinationxe2x80x94preamp (up to 30 dB in 10 dB steps) and two tunable bandpass filters. The unit incorporates novel circuitry that enables the inspector to tune each filter anywhere in the 1.5-7.0 MHz band, the ultrasonic band most commonly used for inspection. The width of the band is also adjustable (low, mid, high) and each filter can either be set to null out a noise signal (xe2x88x9220 dB attenuation applied in the tuned band) or to enhance a desired signal (+15 dB gain applied in the tuned band). One filter can be used to null noise while the other is set to simultaneously enhance a desired signal, or both filters can be set identically to effectively xe2x80x9cdouble upxe2x80x9d on either noise cancellation (via xe2x88x9240 dB total attenuation) or signal enhancement (via +30 dB total gain).
The NSII is connected between the transducer(s) and the pulser/receiver or flaw detector. It is housed in a small (4xe2x80x3xc3x977xe2x80x3xc3x971.5xe2x80x3) enclosure weighing less than two pounds and is powered by either a 9 v battery or AC. It operates in both pulse-echo or pitch-catch/thru-transmission modes. All settings are via detented rotary dials so that the user is assured of repeatable inspections. The unit interfaces with any type of analog or digital ultrasonic unit to provide an add-on enhancement.
The Noise Suppressor II (NSII) combines both PreAmp and Dual Channel Tunable Filter functions. Either function can be used alone or combined. Each of the two filters is tunable in both frequency and bandwidth, and each can either boost (bandpass filter) or cut (notch filter) the signal. The dual filters operate independently and can be tuned simultaneously to different frequencies, for instance 2.25 and 5 MHz, with one acting as an enhancer (e.g., boost the 2.25 MHz desired signal) and the other as a nuller (e.g., cut the 5 MHz unwanted signal).
Another example of using both filters simultaneously is to eliminate noise spikes. Here, one filter (e.g., Channel A) could be used to optimize the desired signal by dialing in its frequency and bandwidth and applying, say, +15 dB boost to create an optimal bandpass filter; the other filter (e.g., Channel B) can be tuned to null the noise spikes by sweeping through the frequency and bandwidth bands to xe2x80x9clock ontoxe2x80x9d the noise and applying a xe2x88x9215 dB cut to this band. It now may be possible to lower the flaw detector""s gain, further reducing the noise level. The present version of the NSII is intended for transducers in the 1.5-7 MHz range. Transducers with up to 10 MHz center frequencies can most likely also be used since the response in a material is often much lower and falls into the NSII""s operating range. Higher and lower frequency units can be made.
The following merely exemplifies, but is not limited to, specifications of the system:
Overall System Frequency Range: Two broadband filters always active to limit the output signal to the 1.5 to 7 MHz range;
By-Pass Mode: Selecting the xe2x80x9cBy-Passxe2x80x9d position completely removes the NSII from the circuitry; the signal can pass through to the Flaw Detector""s screen with the unit either ON or OFF;
Selecting the ON setting for either xe2x80x9cFilterxe2x80x9d position causes the input signal to pass through the circuitry;
PreAmp: 30 dB total unfiltered gain in 10 dB steps (0, 10, 20 and 30 dB).
Tunable Bandpass Filters (identical specs for Channels A and B): Operating Mode: ON or OFF
Frequency: continuously tunable from 1.5 to 7 MHz
Bandwidth: three steps at approximately xc2x10.1 MHz (Low), xc2x10.5 MHz (Mid), xc2x11 MHz (Wide)
Filtered Gain: two steps at +15 dB (Gain) and xe2x88x9220 dB (Null);
Power: Source: one 9 v battery or AC/DC wall converter
Battery Duration: approx. 4-12 hours depending on the number of functions being used; and
Technique for Determining the Optimum Filter Band (for each of the independent filter channels):
1. Turn the Filter ON and set the Gain knob to the Null (xe2x88x9220 dB) position;
2. Sweep the Frequency knob across its band and watch for the desired signal to decrease; manipulate the frequency knob until the signal is minimized to find the signal""s center frequency;
3. Sweep the Bandwidth knob across its band until the signal level further drops to a minimal level;
4. With the optimal filter band so selected, either boost (up to +15 db) or cut (down to xe2x88x9220 dB) the signal. 
Unique features of the new NSII system include:
Add-on module to any UT NDI/E instrument and independent of the UT instrument
Operates in all three NDI/E inspection modes: pulse-echo, pitch-catch and through-transmission;
Operates on single signals in real-time;
Three independent and user-settable functions for noise suppression and/or signal enhancement;
First device to use the well-known State Variable Filter (SVF) design in a novel applicationxe2x80x94UT NDI/Exe2x80x94and in the ultrasonic NDI/E frequency band;
First device to use narrow band variable (i.e., tunable) filters for UT applications;
Ability to tune the filter band in center frequency and width to place the optimal band over the signal of interest;
Capability of simultaneously suppressing noise and enhancing a signal of interest;
Ability to xe2x80x9cdouble upxe2x80x9d either the noise suppression or signal enhancement functions by using both filters with identical control settings;
Use of the preamp function solely as a stand-alone pre amplifier or to boost weak signals prior to the filtering operations;
Small enclosure in a hand-held package; and
Powered by either a 9 v battery or ac adapter.
In other preferred embodiments of the invention is identical in function and uses the same printed circuit board (pcb). The only difference is the frequency covered.
By changing the filters, the new NSII-L covers 0.5 to 2.4 Mhz. xe2x80x9cLxe2x80x9d stands for xe2x80x9cLowxe2x80x9d frequency. The new NSII-XL covers 0.15 to 0.7 Mhz. xe2x80x9cXLxe2x80x9d stands for xe2x80x9cExtra Lowxe2x80x9d frequency.
In a further embodiment NSII-H has the same functions as the above three models, but the circuit, and hence the pcb, is different. The frequency range for the model NSII-H is 8 to 25 Mhz. xe2x80x9cHxe2x80x9d stands for xe2x80x9cHighxe2x80x9d frequency.
That range is able to be changed. The range could be slightly enlarged at both the low and high ends. Changing range only involves changes of filters components on the pcb (as in the -L and -XL models), but the circuit does not change.
The two lower frequency models, NSII-L and NSII-XL, require no circuit layout changes. The circuit topology is exactly the same. Only a few component values change (i.e., resistors and capacitors) in the two filter sections to lower the frequency range to the desired respective level.
These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, and the drawings.